The more complicated the system is, the less reliable. Right? Don't the Trek e-bikes have some kind of proprietary throttle system that has different modes? I think the crystalyte kits are pretty reliable. I've had no problem with mine. There hasn't been many reports of stuff breaking that I'm aware. Well, usually, the weakest part of any e-bike is the controller because that's where the circuit board is and the main guts that control the bike. So I'd worry most about what kind of controller is on the bike and whether that will hold up in the long run. You can find the crystalyte kits at
http://itselectric.ca (they have a US store, too)
If you want reliability, just make sure you don't buy a kit off e-bay.